Fiber optic cables are often used for distributed measurement systems in acoustic sensing applications. Acoustic sensors may be formed by wrapping a segment of fiber optic cable around a core. The length of cable wrapped around the core affects the sensitivity of the sensor.
Pressure changes, due to sound waves for example, in the space immediately surrounding an optical fiber and that encounter the optical fiber, cause dynamic strain in the optical fiber. Optical interferometry may be used to detect the dynamic strain along a segment of the fiber. Optical interferometry is a technique in which two separate light pulses, a sensing pulse and a reference pulse, are generated and interfere with each other. The sensing and reference pulses may, for example, be directed along an optical fiber that comprises fiber Bragg gratings on either side of the core around which the optical fiber wraps. The fiber Bragg gratings partially reflect the pulses back towards an optical receiver at which an interference pattern is observed.
The nature of the interference pattern observed at the optical receiver provides information on the optical path length the pulses traveled, which in turn provides information on parameters such as the strain the segment of optical fiber between the fiber Bragg gratings experienced. Information on the strain then provides information about the event that caused the strain. Analysis of the event allows determination of, for example, a frequency response of the event detected by the sensor. There exists a continued desire to advance and improve technology used in fiber optic sensors.